Ratchet and Clank never managed to assert themselves as the Mario Bros-rivalling mascots Sony has long sought, despite appearing in some memorable titles. Given that their latest outing was marked with little fanfare and slapped with a budget price tag, expectations for Ratchet & Clank: QForce weren't exactly sky high, but it's a surprisingly decent - if a little short-lived - outing.

At first glance, this is a Ratchet & Clank title like any other. It's a 3D platformer with an oversized arsenal, familiar cartoony graphics and a spattering of light RPG elements. While another helping of this wouldn't necessarily have been the worst thing in the world, developer Insomniac Games has added a gaming-changing twist to the formula.

This time around, players have tower defense mechanics to contend with, a gameplay element that has been deeply integrated into the Ratchet & Clank setup. Each level has a QForce base at its heart, and players must ensure it's protected while juggling various mission objectives that have you trekking across the map.

The tower defense elements could have broken the game were they not so well balanced. The object is to protect strategic points within your base from swarms of enemies that attack at intervals. This can be achieved by purchasing traps, such as gun turrets and mines, fighting them off in person, or a combination of both.

Most stages require players to backtrack to their base when an attack alert sounds, but this isn't as frustrating as it might sound. There are teleporters located across the map, so you can always jump back there for a quick skirmish, before returning to where you left off on the battlefield.

Each level's ultimate goal is to activate the planet's defense system, which means penetrating enemy defense shields by attacking and destroying a series of generators. Objectives are straightforward enough to power through in one go, so it's not often that you'll be pulled out of a complex task to attend to the QForce base.

Once the planet's defense has been activated, hordes of enemies descend on the base to test your endurance before the level wraps up.

Ratchet & Clank: QForce offers a surprisingly seamless blend of two genres. The pitfalls of merging tower defense and platforming were many, yet Insomniac has pulled it off well. Unfortunately there is a catch - there are just five stages on offer, meaning the single-player campaign can be bested within five hours or so.

The game relies on difficulty spikes to pad out the experience, respawning enemies, merciless onslaughts on your base, and the need to backtrack to pick up more ammunition and supplies. High score fanatics will find some replay value setting record completion times for perfect runs through each level, and then there's multiplayer.

Both local and online co-op is supported, and these modes are more of a natural fit for the hybrid gameplay. One player can venture out and complete the mission objectives while the other holds the fort back at base, plus you can double team when necessary.

There's also a competitive multiplayer mode, which is full of ideas the single-player campaign would have benefited from. Contests are broken up into three rounds. The first has players claim their territory on the map, while the second sees them gathering resources and amassing an army, and the third is all-out assault.

This robust structure ties in well with the strategically-rich gameplay traditionally found in the tower defense genre, and is the only occasion where Ratchet & Clank: QForce feels like it's fulfilling its full potential.

The Ratchet & Clank series has been around for a decade now, so nobody can blame Insomniac for taking it in new directions. Adding tower defense elements to its 3D platforming infrastructure was an experiment that pays off in some ways, but could have been fleshed out more in others.

Enjoyable multiplayer modes are only worth so much when backed by a paltry single player campaign, but taking the budget price tag into account, we can think of worse Christmas stocking-fillers for fans of the series of the tower defense genre.